1. Field of the Invention
This invention relates to a cylinder liner provided with cooling oil grooves at its outer circumferential surface.
2. Description of the Related Art
In prior art cooling systems for engines, cooling water is normally used for cooling operation. A cylinder block is typically provided with cooling water passages in case of a dry cylinder liner and, in case of a wet cylinder liner, a concave portion formed at an inner circumferential surface of a bore part of the cylinder block and an outer circumferential surface of a cylinder liner define the cooling water passage. The cooling water flows from a lower part of the cylinder liner to an upper part thereof and further flows to the cylinder head to cool the
However, because improvement of engine performance in recent years has become an essential requirement, heat generated in a combustion chamber is also increased and a temperature at an upper part of the cylinder liner near the combustion chamber becomes excessively high. Accordingly, in view of designing engines having a compact size as well as a high speed and a high load capacity, the prior art cooling structure for the cylinder has a problem that the upper part of the cylinder liner near the combustion chamber cannot be sufficiently cooled.
In order to accommodate the foregoing, it has been proposed to provide a cylinder liner in which an outer circumferential surface of the cylinder liner is formed with a plurality of annular grooves, in which the plurality of annular grooves described above are divided into a plurality of groups of annular grooves, where each of the groups of annular grooves has two longitudinal grooves communicating the annular grooves with each other. The two longitudinal grooves forming an outlet and an inlet, respectively, for the cooling oil are disposed at locations spaced apart by 180.degree. in a circumferential direction. The outlet communicates with the inlet in series with the adjoining groups of annular grooves. A total sectional area of the annular grooves in each of the groups of annular grooves is decreased from a lower part toward an upper part in an axial direction of the cylinder liner (referenced in Japanese Utility Model Application No. 62-60967).
With the foregoing, a flow of cooling oil directed from the upper part of the cylinder liner to the lower part thereof will be described, wherein the cooling oil flows around the outer circumference of the cylinder liner through groups of the annular grooves, and thereafter moves from the longitudinal groove forming the outlet of the group of annular grooves toward the longitudinal groove forming the inlet of the adjoining next stage group of annular grooves. The cooling oil then flows from the longitudinal groove into the annular grooves of the group of annular grooves, flows around the outer circumference of the cylinder liner, and then the cooling oil is moved to the lower adjoining group of annular grooves in the same manner.
The cooling oil is then discharged into the oil pan from a discharging longitudinal groove disposed on the extension line of the longitudinal groove forming the outlet of the lowermost group of annular grooves.
In this case, if the cooling oil drops onto the arm part of the crankshaft, the balance weight or the bearing of the connecting rod connected to the pin or the like when the cooling oil is discharged into the oil pan, a substantial flow rate of the cooling oil is flowed down, causing a load to be applied to the rotation of the crankshaft.
In addition, when the cooling oil strikes against the arm part of the rotating crankshaft, the cooling oil is dispersed to mix air during its dispersion and the cooling oil having air mixed therein is dropped into the oil pan. When air is mixed in the lubricant oil stored in the oil pan, the air flows into tee lubricant oil passages or the cooling oil passages together with the lubricant oil, so that the lubricating performance or the cooling performance is reduced.
Accordingly, the cooling oil to be discharged into the oil pan is preferably dropped onto the main shaft of the crankshaft.
However, if the circumferential positions of the longitudinal groove forming the outlet of the lowermost group of annular grooves are disposed above the main axis of the crankshaft, the longitudinal groove forming the inlet for the cooling oil in the group of annular grooves is disposed above the main axis of the crankshaft.
In the case of a multi-cylinder type engine, there is a problem that an arrangement of the inlets for the cooling oil above the main axis of the crankshaft causes the supplying passages formed in the cylinder block for supplying the cooling oil to the inlets for the cooling oil to be bypassed around bolt holes, and a formation of the supplying passages for the cooling oil extending from the side surface of the cylinder block to the inlets for the cooling oil in the cylinder liners is not facilitated due to the fact that the bolt holes used for fastening the cylinder liners to the cylinder block are disposed at the lateral positions between the bores of the cylinder block.